Offshore systems (e.g., in lakes, bays, seas, oceans and/or the like) often include a riser which connects a surface vessel's equipment to a blowout preventer at a subsea wellhead. Offshore systems which are employed for well testing operations may also include a safety shut-in system which automatically prevents fluid communication between the well and the surface vessel in the event of an emergency, such as when conditions in the well deviate from preset limits. The safety shut-in system may include a subsea test tree which is landed inside the blowout preventer on a pipe string. The subsea test tree generally includes a valve portion which has one or more safety valves that can automatically shut-in the well via the safety shut-in system.
During well completion installation, intervention and testing activities, a test tree is lowered into a riser from a surface location and landed in a blowout preventer above the well. Valves on the subsea test tree and completion valves are hydraulically operated in one of two ways. First, the valves can be fully hydraulically operated. A hydraulic power unit located at the surface location uses hydraulic pressure both to send control signals to the test tree and to open and close the valves located on the test tree. Second, the valves can be electro-hydraulically operated. An electrical signal is sent to a control circuit subsea. When the subsea control circuit receives the electrical signal to open or close the valves, hydraulic pressure is provided from the surface hydraulic power unit to open and close the valves in response to such electrical signals.